Carbon nanotubes are quasi-one-dimensional nanostructures and were first reported in an article by Sumio Iijima entitled “Helical Microtubules of Graphitic Carbon” (Nature, Vol. 354, Nov. 7, 1991, pp. 56-58). Carbon nanotubes have been highlighted as a new functional material expected to have many microscopic and macroscopic applications. Extensive research has been conducted into using carbon nanotubes in various applications, for example in electron emission devices, etc.
Typical electron emission devices incorporating carbon nanotubes each includes a cathode with carbon nanotubes acting as electron emitter formed thereon, and a counter anode with a phosphor layer formed thereon. Emission current can be obtained by applying a voltage difference of a few hundred volts to a thousand volts between the cathode and the counter anode which are received in a vacuum space. The strength of an emission current can be varied with the variation of the magnitude of the voltage difference.
Generally, it is impractical to adjust the strength of the emission current due to the large voltage difference applied between the cathode and counter anode. In addition, molecules accumulated at the carbon nanotubes may contaminate the carbon nanotubes which results in large fluctuation in the emission current, even causes the loss of the electron emission capability of the carbon nanotubes. Therefore in order to achieve an emission current with relatively high stability, it is necessary to operate the carbon nanotubes formed on the cathode at a much higher vacuum ranging from 1×10−9 to 1×10−8 millibars (1 millibar=100 pascals). However, this high vacuum maintenance will inevitably result in the increase of cost of the electron emission devices.
What is needed is to provide an electron emission device with a practically adjustable and relatively stable emission current, and method for generating such an emission current.